Dormant states of organisms are easier to store than the living statebecause they tolerate larger variations in temperature, light, storage space etc., making them attractive for lab culture stocks and also for experiments under special circumstances, especially space flight experiments. Like several other organisms, Euglena gracilis is capable of forming desiccation tolerant resting states in order to survive periods of unfavorable environmental conditions. In earlier experiments it was found that dormant Euglena cells must not become completely desiccateed. Some residual moisture is required to ensure recovery of the resting states. To analyze the water demand in recovery of Euglena resting states, cells were transferred to a defined amount of cotton wool (0.5 g). Subsequently different volumes of medium (1, 2, 3, 4, 5, 8, 10, and 20 mL) were added in order to supply humidity; a control was set up without additional liquid. Samples were sealed in transparent 50 mL falcon tubes and stored for 9 months under three different conditions:

Constant low light conditions in a culture chamber at 20° C,

In a black box, illuminated with short LED-light pulses provided by joule thieves, and

In darkness in a black box.

After nine months, cells were transferred to fresh medium and cell number, photosynthetic efficiency, and movement behavior was monitored over 3 weeks. It was found that cells recovered under all conditions except in the control, where no medium was supplied. Transcription levels of 21 genes were analyzed with a Multiplex-PCR. One hour after rehydration 5 of these genes were found to be up-regulated: ubiquitin, HSP70, HSP90, the calcium-sensor protein frequenin and a distinct protein kinase (PKA), which is involved in gravitaxis. The results indicate a transient general stress response of the cells.